The present disclosure is directed to an improved drill bit which is adapted to be used in drilling in coal mines and other similar shaft mines. It also can be used in open pit mining in a fashion which will be set forth. Briefly, safety and security of a mine often requires that a number of relatively shallow holes of small diameter be drilled into the wall of the shaft. It is not uncommon to drill vertically in underground shafts up into the overburden as a preliminary step to anchoring shoring in the mine to enhance safety for the miners. In coal mines, this often requires drilling perhaps 4 feet with a drill bit to form a hole about 4 feet in depth which is subsequently provided with an anchor rod of about 1 to 3 inches in diameter. It is not uncommon to deplete a drill bit after only about 50 holes are drilled with the bit. The drill bit must then be discarded and a new drill bit used. The present disclosure sets forth an improved drill bit which is able to provide much greater life. A fair estimate is that the improved drill bit of the present disclosure can provide at least four times as many anchor holes in the typical coal mine compared with an old drill bit of construction in accordance with prevailing technologies heretofore.
The drill bit of the present disclosure is an improved spade drill bit. It has a support body mounted on a stem. The stem is suitably connected with a chuck and drive motor which imparts rotation. The stem connects to a drill bit body which is provided with a transverse groove. The body serves as a support and also an alignment guide for a spade which is positioned in the groove. The spade resembles a typical shovel and in that sense provides the nonmenclature for this type of drill bit. The spade shaped drill bit is constructed with a planar spade which is held in the transverse groove in the drill bit body. The spade is equipped with two side edges which provide the gauge measurement for the drilled hole. The spade is welded or brazed to the body of the drill bit and is aligned so that it is centralized on the body for easy control of the hole diameter. In addition to that, the spade is constructed with two generally planar faces which come to a point. The angle at the point is not sharp i.e. the included angle between the two faces defining the point is relatively large, about 120.degree.-150.degree..
The two planar faces which come together at the point of the spade extend outwardly at the included angle and terminate at the gauge defining side faces. The side faces define a relatively sharp point with the exposed leading planar faces. The sharp point is able to cut material but most of the wear accumulates in the immediate vicinity of the corners at the side faces. They wear rapidly in comparison with other parts of the spade. This rapid wear is one source of destruction of the spade drill bit so that ultimate replacement is required. One aspect of the present invention is the incorporation of an insert which is joined to the spade to reinforce and make stronger the spade at that region so that the drill bit lasts much longer.
In one version of the present invention, a segment of a circular disk of polycrystalline diamond compact (hereinafter known as PCD) is inserted at the corner. The entire corner is therefore made of PCD material. This extends the life and maintains a true gauge cutter for much longer. In addition to that, an alternate embodiment utilizes PCD formed in the shape of a chevron which has an angle suitable for incorporation at the corner. By using this corner angle, the side faces can be clad with protective material, and this protective material can be extended along the exposed cutting faces. Again, this substantially extends the life of the device.
The spade as improved in accordance with the present disclosure is affixed to the drill bit body. The improved spade thus extends the life so that the user need not replace the drill bit as often. Moreover, because the improved spade with PCD is incorporated at both the cutting edges and on the side faces, a gauge hole is assured in ordinary operation.